DHCP Troubleshooting Process

-

DHCP Process DORA

D- Discover --> A device sends broadcast message to find DHCP servers

O- Offer --> DHCP server responds and offer IP addresses and further details to the device

R- Request --> device selects IP address and send request to accept the offer

A- Acknowledge --> The DHCP server acknowledges the IP address lease

 

Reconnaissance: Need to assess the issue facing according to the Network Topology & configuration, whether the issue facing by any Individual/Everyone/specific group pf People (People related to same VLAN/department)

 

Troubleshooting:

  1. If the issue is facing by all set of users
    + the issue is mostly resides in the DHCP server scope, start by checking the server up status and reachability and DHCP configuration.
    + check/confirm Relay-agent configuration that the correct IP address (server) configured on the correct interface as helper-address.
        Lab Eg: (R1) ip helper-address 10.2.2.1 --> this is configured on the default gateway   
        interface of the internal router
    + check the DHCP pool whether the IP address ranges are still available to lease or not. Check/confirm the DHCP excluded address range is correct
        Command we can use in Cisco Environment:
        - sh ip dhcp pool --> confirm the count of leased addresses are less than Total addresses
        - Lab Eg: ip dhcp excluded-address 10.1.1.254 --> if the range is incorrect make necessary changes. Note: Exclude default gateway address
    + check the default route configured on the DHCP server to route the traffic to different subnet (helpful while the server resides on different subnet than internal). If this is not configured, we observe continuous Discover debug messages. Please refer the attached image for more clarity Fig: DORA Wireshark capture
        Lab Eg: ip route 0.0.0.0 0.0.0.0 10.2.2.254
     
  2. If the issue facing by any individual
    + start by checking L1- physical link status, whether broken or not.
    + check/confirm the particular switch port the user is connecting is tagged under appropriate VLAN
       command used in Cisco Environment:
       - sh vlan bri --> view the all vlans configured with the corresponding allowed interfaces
    + check if there's any port security configured on the interface where the connected user unable to get the DHCP IP address
  3. If the issue is facing by People related to same VLAN/department
    + check the DHCP network is same subnet as IP address configured on the VLAN
    + ensure all the interfaces are in the same corresponding VLAN and ip helper-address is configured in case the DHCP server residing in different subnet on the corresponding interface
    + ensure the Trunk links are configured correctly over the switch in order to get the all traffic
        command used in Cisco Environment:
        - sh int trunk --> view the trunk interfaces
  4. Rest Troubleshooting
    regardless of the severity whether issue facing by any Individual/Everyone/specific group pf People below steps we can follow
    + DHCP Misconfiguration
    + check  DHCP pool out of IP addresses and confirm the excluded address range as well
    + Duplicate IP address
    + DHCP snooping

 

Lab Configurations:

DHCP server: configured dhcp server here with IP address of 10.2.2.1/24 and default route

ip dhcp excluded-address 10.1.1.254

ip dhcp pool internal

 network 10.1.1.0 255.255.255.0

 dns-server 10.2.2.1

 default-router 10.1.1.254

 domain-name www.xyzsolutions.com

 

 ip route 0.0.0.0 0.0.0.0 10.2.2.254

R1: the router which works as a relay agent to the network 10.1.1.0/24

configured Fa0/0: 10.2.2.254/24 end connecting to dhcp server

                    Fa0/1: 10.1.1.254/24 end connecting to internal devices

                                  ip helper-address 10.2.2.1





Comments

Post a Comment

Popular posts from this blog

Understanding Titanic Survival Predictions with Decision Trees

-
Image
  Decision Tree: Supervised learning Algorithm Can do both Regression and Classification capabilities Inverted tree like structure with bunch of if-else statements The Titanic dataset is one of the most famous case studies in data science. It captures passenger details such as age, sex, class, fare, and family aboard, along with whether they survived or not. In this post, we’ll walk through how a decision tree model uses these features to predict survival, and what the visualization reveals. How the Decision Tree Works Note: These features are based on the importance table at the right side Root node: “Was the passenger male?” If female , survival chances are much higher. The tree then considers passenger class and fare to refine predictions. If male , survival chances drop significantly, but age and family aboard (siblings/spouses) still play a role. Each node in the tree shows: Gini impurity: How mixed the group is (lower / purer). Samples: Number of passengers in that group. ...
Read more

From Raw Logistics Data to Business Insights: An Excel Analytics Project (RFM Analysis)

-
Image
Analyzed logistics shipment data in Excel to evaluate delivery performance, cost, transit time, distance trends. Extended the analysis with RFM-based carrier segmentation to understand carrier utilization and spending patterns, supporting more data-driven operational decisions. My objective was to explore two practical business questions: How are delivery delays and shipment outcomes behaving across time and distance? How can carrier performance be evaluated using cost, transit time, shipment activity, and delivery performance? Starting with data quality I first reviewed the dataset for completeness and consistency. The initial cleaning process included identifying missing delivery dates and transportation costs, checking transit-day inconsistencies, and investigating numerical outliers. One thing I wanted to avoid was treating every unusual value as bad data. After null-value treatment, the working dataset contained 1,928 shipment records , while the dataset used after the selected ...
Read more

Unable to access the PaloAlto VM image via HTTPS

-
Image
Recently, I encountered an Issue of "Unable to access the PaloAlto VM image via HTTPS". Here's how I applied troubleshooting steps to resolve it: Configuration Changes done before: Configured static management IP & default gateway and rebooted the PA VM, then faced the issue. Observed: Unable to access the PaloAlto VM image via HTTPS. Unable to ping to the default Gateway from the PA and viceversa. Error- getting Destination Host Unreachable in both cases. Analyzed: + Checked the Management IP address and netmask, both are same as bridged network (physical) + Checked the default route "show routing route" - no route configured + While pinging from the base machine to PA and vice versa getting error as "Destination is Unreachable". Hypothesized: + As per the Error message, primarily issue is Network related, that the PA VM is unable to reach physical NIC IP. Tested: + Tried with changing the management IP address within the same subnet (as physic...
Read more